La Partage and En Prison: the roulette rules that halve the edge
La Partage returns half of an even-money stake when the ball lands on zero. En Prison holds the stake for the next spin instead. On a single-zero wheel both cut the house edge on those bets from 1/37 (about 2.70%) to 1/74 (about 1.35%). Neither rule touches other bets.
The problem these rules address
On a single-zero wheel the green 0 is the only pocket where an even-money bet loses without the colour or parity being wrong. Of 37 pockets, 18 win and 19 lose, and one of those 19 is the zero. The standard edge of 1/37 comes entirely from that zero, as set out in the guide to the roulette house edge.
La Partage and En Prison are two rules that soften what the zero does to an even-money bet. They are rules of the table, not strategies for the player: the operator sets them, and the player either has them or does not.
The two rules in plain terms
La Partage (French for "the sharing") splits the stake. When zero lands, half of an even-money stake is returned and half is lost.
En Prison (French for "in prison") holds the stake. When zero lands, the stake stays on the layout for the next spin. If the held bet wins on that spin, the stake is released and returned, with no winnings added. If it loses, it is lost. If zero lands again, it is held again.
Both apply only to the even-money chances: red or black, odd or even, high (19 to 36) or low (1 to 18). Bets on numbers, splits, dozens and columns are paid and lost as usual.
Deriving the La Partage edge
Stake one unit on red on a single-zero wheel. Eighteen pockets win one unit, eighteen lose the unit, and one (the zero) returns half a unit, which is a loss of half a unit.
(18/37 × 1) − (18/37 × 1) − (1/37 × 1/2) = −1/74 ≈ −1.35%
The standard result is (18 − 19)/37 = −1/37, about −2.70%. La Partage takes the loss on zero from a full unit to half a unit, so the edge is exactly half of what it was. The expected value per unit staked is −1/74, and the return to the player is 73/74, about 98.65%, against 36/37, about 97.30%.
Deriving the En Prison edge
The held stake is worth something, so first find what a held stake is worth. Let V be the expected result, per unit, of a bet that is currently in prison. On the next spin there are three outcomes:
- The bet wins (probability 18/37): the stake is released, net result 0.
- The bet loses (probability 18/37): the stake is lost, net result −1.
- Zero lands (probability 1/37): the stake is held again, and its worth is V once more.
That gives a recursion, and it can be solved directly.
V = (18/37 × 0) + (18/37 × −1) + (1/37 × V)
V × (1 − 1/37) = −18/37
V × 36/37 = −18/37
V = −1/2
A held stake is worth exactly half a unit less than a fresh one, the same as the half-back on zero under La Partage. Now the full bet: 18/37 wins one unit, 18/37 loses one unit, and 1/37 goes to prison with value V.
(18/37 × 1) − (18/37 × 1) + (1/37 × −1/2) = −1/74 ≈ −1.35%
So En Prison in its repeating form has the same average cost as La Partage. The arrangement is symmetric: whenever the stake is decided, winning and losing are equally likely among the non-zero results, so the held stake is lost half the time and recovered half the time.
The rules compared
| Even-money bet, rule applied | Loss on zero | House edge (exact) | House edge (decimal) | Return to player |
|---|---|---|---|---|
| Single zero, no special rule | Whole stake | 1/37 | 2.70% | 36/37, about 97.30% |
| Single zero, La Partage | Half the stake | 1/74 | 1.35% | 73/74, about 98.65% |
| Single zero, En Prison held until decided | Half a unit on average | 1/74 | 1.35% | 73/74, about 98.65% |
| Single zero, En Prison for one spin only (a second zero loses the stake) | 19/37 of the stake on average | 19/1369 | 1.39% | 1350/1369, about 98.61% |
| Double zero, no special rule | Whole stake | 2/38 = 1/19 | 5.26% | 18/19, about 94.74% |
| Double zero, half back on both 0 and 00 | Half the stake | 1/38 | 2.63% | 37/38, about 97.37% |
The one-spin En Prison row follows from the same method. A held stake is released on a win (18/37, result 0) and lost on a loss or on a second zero (19/37, result −1), so V = −19/37 and the edge is (1/37) × (19/37) = 19/1369. The wording of the rule changes the number, which is why the exact rule text matters.
Why the number is lower but the cost is not zero
An edge of 1/74 is still an edge. Every unit staked costs 1/74 on average, and the cost still grows with the total staked. What the rule changes is the size of the multiplier, not the fact of it.
A player stakes KES 100 on red for each of 100 spins, KES 10,000 in total. With no special rule the expected loss is 10,000 × 1/37 = KES 270.27. With La Partage or repeating En Prison it is 10,000 × 1/74 = KES 135.14.
Zero lands about 100/37, or 2.7 times, in 100 spins. Each time, La Partage returns KES 50 of the KES 100. The saving is about 2.7 × 50 = KES 135 on average, which matches the difference between the two figures.
These are averages over very many spins. A session of 100 spins can finish well above or below them, as the guide to house edge and RTP explains.
What is different in play
The average cost is the same, but the two rules feel different. La Partage settles the zero immediately. En Prison leaves the bet open, so the player waits one or more spins for a result and, on average, a held stake needs 37/36 of a spin to resolve.
En Prison also changes the tidy "one spin, one outcome" rhythm. A stake can be held for several spins in a row, with probability 1/37 each time the wheel is spun. That makes the result of any one bet slightly harder to follow, not more favourable.
What these rules cannot do
A lower edge does not turn roulette into a game that can be beaten. The expected result of every bet is still negative, and a sum of negative bets is negative. Doubling after a loss does not repair this, as the Martingale analysis shows: the edge is simply 1/74 of a staked total that doubling makes larger.
The rules also do nothing for number bets. A player who bets straight up on a La Partage wheel still faces 1/37 on that bet. Nor does either rule make a spin depend on the one before it, a point covered in the gambler's fallacy and session limits.
Checking which rule a table uses
Names are not reliable. A table can be called "French roulette" and still not offer either rule, and two tables with the same name can differ. The reliable source is the rule text displayed for the game, which fixes how zero is treated, whether the rule covers both zeros, and how long a stake is held.
Regulation 20(2) of the Gambling Control (Conduct of Gambling Operations) Regulations, 2026 says a licensee shall "display clearly rules of games, odds, house edge and average return to the player". Regulation 20(3) applies the same regulation to online gambling, with necessary modification. Compare the displayed house edge with the figures in the table above: a single-zero wheel showing about 1.35% on even-money bets is using one of the two rules. For the wheels themselves, see European and American roulette.
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Questions and answers
What is La Partage in roulette?
La Partage is a rule for even-money bets (red or black, odd or even, high or low). When the ball lands on zero, half of the stake is returned to the player and half is kept by the house. All other results are paid as usual.
What is En Prison in roulette?
En Prison is a rule for even-money bets. When zero lands, the stake is not lost but held for the next spin. If the bet then wins, the stake is released without a win; if it loses, the stake is lost; if zero lands again, it is held again.
Which is better for the player, La Partage or En Prison?
In average cost they are identical when En Prison keeps holding the stake until it is decided: both give a house edge of 1/74, about 1.35%. En Prison variants that end the holding after one spin cost slightly more, and the experience differs because En Prison takes extra spins to resolve.
Do these rules apply to a straight-up number bet?
No. Both rules are defined for even-money bets only. Straight-up, split, street, dozen and column bets keep the full edge of 1/37 on a single-zero wheel.
Do double-zero wheels use La Partage?
The standard double-zero edge is 2/38, about 5.26%. If a table did apply half-back to both green pockets on even-money bets, the edge would be 1/38, about 2.63%. The rules shown for the game state whether any such rule exists.
Where can a player find out which rule a table uses?
In the rules of the game. Regulation 20(2) of the 2026 operations regulations requires a licensee to display clearly the rules of games, odds, house edge and average return to the player.